This invention relates generally to poultry slaughtering.
Today, it is common to "process" (slaughter and butcher) fowl such as chickens in factories devoted to the purpose. Typically, chickens are carried by moving foot shackles first through an electrical stunning apparatus, which immobilizes each bird but does not kill it, and immediately thereafter over a blade which cuts the blood vessels of the neck. The heart assists in removing blood from the circulatory system.
Thorough bleeding is necessary to avoid objectionable dark blood vessels in the meat, so it is best not to decapitate the bird, or otherwise injure the spinal cord initially, since such injuries may arrest the heart prematurely.
Another reason for avoiding injury to the spinal column is that injuring the spinal cord induces shock in the bird, closing the pores of the skin so that the feathers are held tightly, thereby complicating the subsequent feather picking operation. One can compensate for this response by increasing the scalding temperature or duration, but overscalding adversely affects qualities including skin color. Shock also reduces the bleeding rate, as it constricts the blood vessels.
A further consideration is that is important not to cut the trachea, because suffocation can result from blood entering the trachea.
One purpose of electrically stunning chickens is to immobilize them so that an accurate neck incision can be made. However, there are some objections to stunning, on various grounds. One could avoid these objections if one could kill chickens and other fowl automatically, but without requiring an advance electrical stunning step. The problem addressed by this invention is that the necks of birds which have not been are difficult to cut automatically with precision.
Prior inventors have developed a number of devices for immobilizing birds during slaughtering. One such device is disclosed in Martin's U.S. Pat. No. 3,571,845. That device includes a foot shackle conveyor that runs above an endless chain loop moving at about the same speed. The chain supports a series of flat blades, like pickets, between which the bird's heads are captured en route to the cutting blade.
Since the writing of the prior Martin patent, the neck incising operation has become mechanized, freeing workers from this unpleasant task. But because the machinery now used is not as adaptable as the workers it replaced-that is, it cannot alter its blade position to compensate for the movements of individual birds-it is necessary to ensure that the birds are passed over the cutting blades in a fixed, reproducible orientation. It might be thought that a live bird would present a random moving target during this process; however, we have found that birds respond to certain stimuli in predictable ways, and that these responses can be used to improve the operation of killing machinery. This observation has led to certain aspects of the invention described below.